It depends on the level and build but my rule of thumb is less to none for run blocking and more for pass blocking but strength, blocking, and agility are more important. I might even go as far as saying confidence is more important.
Here is how I choose.
LOT most blocking, agility and protect SA. Actually the Protect SA tends to sway my choice the most.
ROT is the OT that just missed LOT or the strongest.
RG is the strongest and fastest. The LG is the G that just missed RG or the better blocker to pick up blitzes in the passing game.
The C doesn't matter. I only have two on any team and never use any other player for a C.
Basically OTs play OT, Gs play G and Cs play C. The positions are very unique but if I were to play a player out of position it would be a C at G. Thats about it.